In recent years, there grows a demand for a printed board on which electronic components are mounted with high density along with size reduction and performance enhancement of electronic devices. Most of the printed boards have a complicated shape following a shape of an electronic device. In addition, if the electronic device is a cell phone, for example, various printed boards are manufactured in accordance with various forms of cell phones.
However, in the case of automatically mounting electronic components, if the specification of a mounting device is changed in accordance with the shape of a printed board, a cost of equipment increases. To that end, a multicavity molding substrate of a predetermined rectangular shape is generally prepared to build printed boards for plural electronic devices.
At this time, since the multicavity molding substrate is rectangular and the printed board has a shape following each electronic device, a frame-like, unnecessary portion (hereinafter referred to as frame-like unnecessary portion) inevitably remains at the outer periphery of the printed board on the multicavity molding substrate. Therefore, at the time of mounting the printed board to the electronic device, an operation for separating the frame-like unnecessary portion from the printed board is preferred.
To describe a method for separating the frame-like unnecessary portion from the printed board, a groove is formed in a portion intended to separate at the outer periphery of the printed board and in addition, a connection for connecting the printed board and the frame-like unnecessary portion is formed in several positions. Then, after automatically mounting electronic components onto plural printed boards built on the rectangular multicavity molding substrate, and then, mounting each printed board to an electronic device such as a cell phone, the connection is taken off. As a result, the printed board is separated from the frame-like unnecessary portion into a single piece and mounted onto the electronic device.
To give specific methods for removing the connection, there are known (1) a manual division method for manually cutting off the connection portion, (2) a mold division method for cutting the connection using a mold with a press machine, and (3) a router bit division method for cutting and removing the connection with a router bit.
As for (1) the manual division method, however, a man power and operation time remain a major obstacle to enhancement of productivity. Further, as for (2) the cutting method with a press machine, although productivity can be increased, an expensive mold is prepared for mounted printed boards of various shapes, which inevitably involves an increase in cost for equipment.
In contrast, as for (3) the router bit method, since productivity is high upon the removal, and a requisite cost of equipment can be reduced, this method is widely used for processing separating a printed board from a frame-like unnecessary portion as discussed in Japanese Laid-open Patent Publication No. 2001-156423. In the case of separating the printed board from the frame-like unnecessary portion based on the router bit method, division processing is performed under such conditions that a multicavity molding substrate being put on a jig called a substrate holding pallet is inserted to a printed board processing apparatus (hereinafter referred to as substrate processing apparatus) as discussed in Japanese Laid-open Patent Publication No. 2001-156423.
Here, the router bit is a consumable item, which wears out with time and decrease its diameter. Up to now, if a router bit wears out by a predetermined amount or more, the worn router bit is discarded and replaced with a new router bit.
A router bit used in the above substrate processing apparatus includes a cylindrical (bar-like) bit. Further, the cutting length of the router bit is about 4 to 5 mm if the diameter is φ1 mm. Meanwhile, the thickness of a substrate to be processed is generally about 0.5 mm.
Further, the router bit is a consumable item, which wears out with time due to substrate processing and decreases its diameter. The worn router bit cannot appropriately process a substrate. To that end, if the router bit wears out beyond a predetermined ultimate wearing amount, up to now, the worn router bit is replaced with a new router bit.
According to a conventional method, processing is generally performed at a predetermined processing position of a router bit. Thus, in the case where a depth of wear in the predetermined processing position exceeds the ultimate wearing amount, even if a bit portion other than the processing position does not wear out, the router bit is replaced with a new one. As described above, the conventional method is low in usability of the router bit, resulting in problems of shortening a substantial service line of the router bit and increasing a running cost for substrate processing.
On the other hand, proposed is the structure that holds two substrates to be processed at different levels and processes the substrates using two different portions of a router bit to thereby efficiently use the router bit. Even with this structure, however, a bit portion of the router bit partially remains unused. Thus, it is difficult to say that the router bit is efficiently used.